In the space applications, it is necessary to be able to orient certain elements of a satellite or of a spacecraft, such as an antenna or a mast, in a predetermined direction, in order, for example, to direct them toward a fixed star, retain an aim toward a point on the surface of the Earth, or even scan a particular area on the surface of the Earth or of any celestial body. On the same principle, it is necessary to position a satellite when placing it in orbit. A satellite is propelled by one or more jets for electrical propulsion or for chemical propulsion. The terms electrical jet or chemical jet are also used. The orientation of each jet makes it possible to position the satellite in the desired position. It is therefore necessary to orient each jet as a function of the desired position of the satellite. Each jet is oriented using a device called an aiming device.
These days, the new jet aiming devices for electrical propulsion need to be made reliable and to be more competitive in terms of costs and lead times. For this, it is necessary to be able to reduce the number of components of the aiming device, which has a direct effect on the cost reduction, and on the manufacturing and assembly, integration and testing time.
Currently, the jet aiming devices for electrical propulsion are composed of a motorized universal joint offset relative to the mass to be moved, that is to say relative to the jet and to the plate on which the jet is fixed. Such a configuration demands the presence of an additional stacking mechanism to keep the assembly in the stacked configuration. This is because the satellite launch phase is accompanied by vibrations, and it is therefore necessary to keep together the assembly formed by the offset plate and the jet during the launch phase through a stacking mechanism.
The specifications require the propulsion components to be positioned in a certain specific configuration so as to be able, in case of failure of the stacking mechanism, to operate in degraded mode. This requirement dictates variable positions of the components depending on the various types of platforms on which the aiming devices are mounted. A standard stacking mechanism prevents this type of multiple-position mounting.
Similarly, for the adjustment and test phases on the ground prior to the satellite launch, it is necessary to be able to move the jets into extreme positions to check that the components are operating correctly. The torque generated by the offsetting of the jets exceeds the motor drive capability of the gear motors and dictates the use of complex and costly compensation mechanisms.
Finally, the installation of a stacking mechanism results in a cost overhead and a significant increase in the weight on the satellite, which runs counter to the desired solution.